Last night I downloaded and played Cannon Smash. I was quite impressed - the ball movement is good, the gameplay fast and fluid. The graphics, although quite simple, are quite nice as well when in motion.
The main problem with this game, and what would be a good mini-project for a budding developer, is the controls. Currently you use the LMB to hit backhands, the RMB to hit forehands, and a slew of keys to target a point on the other side of the table. It's unwieldy - it takes a while to get used to hitting the correct mouse button and at the same time varying the destination of the ball - but, once mastered, it's not even skillful. All you need to know are the far corners (1 and 7) and to be able to time your forehand (RMB). The controls are complex enough to confuse, but once understood are not powerful enough to realistically model table tennis. It's a shame because the ball physics and presentation are really good.
I think it an autochoice of forehand/backhand (depending upon which target is closest to the path of the ball) and instead have the mouse buttons instead represent types of shot - LMB topshin, RMB slice. Aiming should be done by lateral mouse movement whilst a mouse button is depressed. Slice variance should be done by movement of the mouse forwards or backwards whilst a button is depressed. Foot movement should be done by mouse movement whilst no buttons are pressed. That describes a set of controls that would require skill to truly master and offer a massive variation on gameplay that fairly well describes the game of table tennis. The only aspect not covered, really, is shot depth.
Add some better player models, perhaps characters of some sort instead of faceless manikins, more variation on the degrees of skill of AI opponents, and a tournament mode, and Cannon Smash would be a superb Free Software game. As it is, it's just a good Free Software game. :-)